This is a question that is brought up quite often here and you will find many different answers depending on the target device. I would recommend searching both the workshop and the epub threads to see all the pro's and con's for each technique.
My personal favorite is using the svg wrapper code that you mentioned. It does take a little bit of study to understand, but it isn't too bad. The svg wrapper will allow you to properly scale an image to fill the whole screen while keeping the proper aspect ratio.
The height portion of <img> is not reliable - so I only use <img> for inserting images of a specific size onto a page.
Cheers,